Japan, the only major market for urchins, keeps thorough records on where each catch came from.

Jim Wilson is an economics professor with the School of Marine Sciences at the University of Maine in Orono.

"Because of the peculiar nature of the market and the animal, you can see very clearly when and where this spatial expansion has occurred, moving from resource to resource as depletion takes place," he said.

Following the collapse of the cod fishery in Maine (see map) in the mid-1980swhich removed the urchins' main predatorthe local population of green sea urchins grew rapidly.

In 1987 an unregulated urchin harvest began off the Maine coast.

Within just six years of targeting by the sushi market, the region's urchin population was devastated.

Deep-sea fisheries take even less time to disappear than coastal populations, Worm says.

Fishers often work a chain of deep-sea mountains for usually no more than two or three years before they destroy the local population of fish and move on.

"People are just beginning to realize what is down there, and it is being scooped up indiscriminately by people who act exactly like roving bandits," he added.

Common Good

Economist Mancur Olson originally coined the term "roving bandits" as part of an argument about the origins of government.

He imagined a world full of roving bandits, who arrive in one place and take what they can before moving on.

But if the bandits are forced to stay in one place, they will "have to rethink the game entirely," Wilson said.

"I think of it in terms of Vikings roaming around, looking for places to raid and pillage," he added.

"If one group of Vikings suddenly found themselves stuck in one place because their boat was wrecked, all of a sudden they'd be faced with the problem of how do they treat the local people."

The study team agrees that emphasizing the common good of protecting resources is one way to combat roving bandits.

"I think we are neglecting the importance of the local level backed up by national laws," said University of Manitoba, Canada, professor Fikret Berkes.

Local people need property rights over local resources to provide them with incentives to conserve those resources, he added.

Tropical reef researcher Terry Hughes, who convened the group of experts, believes part of the solution lies with the consumer.

People can "refrain from eating species which are threatened or those that play a particularly important role in the functioning of an ecosystem," he said.

Disrupting the population of a single marine species can have dramatic consequences on the whole ecosystem.

"It's like hitting one of the main distributor lines in a power grid," Worm, the Dalhousie University biologist, said.

"When you pull out nodes or cables from the power grid at random, sometimes you will hit a really important one, and the lights will go out all over the place."